In recent years, it has been considered to be important to elevate consciousness of global environmental issues (i.e., consciousness of global environmental issues has risen), and take measures against global warming, and it has been desired to clean automotive exhaust gas taking account of its effects on the environment. It is known that the capability to clean automotive exhaust gas is affected by the performance of automobiles and the composition of gasoline. In particular, the petroleum refining industry is required to provide high-quality gasoline.
Gasoline is produced by blending a plurality of gasoline blend stocks obtained by a crude oil refining process. In particular, a gasoline fraction obtained by subjecting a heavy hydrocarbon oil to a fluid catalytic cracking reaction (hereinafter appropriately referred to as “FCC gasoline”) is incorporated in gasoline in large quantities, and considerably affects the quality of gasoline.
The heavy hydrocarbon oil catalytic cracking reaction is a reaction that converts low-quality heavy oil obtained by a petroleum refining process into light hydrocarbon oil through catalytic cracking. When producing FCC gasoline, hydrogen, coke, liquid petroleum gas (LPG), light cycle oil (LCO) (i.e., middle distillate), as well as heavy cycle oil (HCO) and slurry oil (SLO) having a boiling point higher than that of LCO (i.e., heavy distillate) are produced as by-products.
Along with the recent structural changes in oil demand, it has been desired to increase the production of light olefins (e.g., propylene and ethylene) that are used as a petrochemical feedstock. The light olefins are mainly produced by cracking a heavy hydrocarbon oil using a thermal cracker or a fluid catalytic cracker, for example.
However, the yield of light olefins achieved by cracking a heavy hydrocarbon oil using a thermal cracker is low. Moreover, since the yield of light olefins considerably changes depending on the feedstock, it is difficult to deal with the current increase in demand.
A method that adds a high-silica zeolite having high acidity (e.g., ZSM-5) to a catalyst to increase the light olefin content in FCC gasoline and improve the octane number of FCC gasoline has been proposed as a method for cracking a heavy hydrocarbon oil using a fluid catalytic cracker (see Patent Document 1 (JP-A-60-208395)). However, this method has a technical problem in that the yield of a heavy distillate also increases, and it is difficult to implement an effective cracking reaction.